FEB 2 1994 |
OFFICE OF NAVAL RESEARCH
1 October 1903 through 31 December 1993
GRANT No. : N00014-89-J-1754
THE EFFECTS OF MAGNETIC STORM PHASES ON
F LAYER IRREGULARITIES
FROM AURORAL TO EQUATORIAL LATITUDES
Jules Aarons and Michael Mendillo, Co-Principal Investigators
Center for Space Physics
Boston, MA 02215
Reproduction in whole, or in part, is permitted for any purpose of the United
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EQUATORIAL AND MIDDLE LATITUDE STUDIES
During this quarter there was the start of an extensive review of the literature
on middle latitude irregularities. In earlier reports we have noted the levels of irreg¬
ularities at latitudes above the equatorial anomaly region (within 15 degrees of the
magnetic equator) thru our analysis of a few examples of raw data from Osan, Korea.
We then began to reduce and analyze data from Puerto Rico and Hawaii using 136
MHz scintillation data taken during both high and low solar flux years. At the levels
that can be noted (peak to peak excursions of 15-20 dB) there is considerable activity.
In order to place the data into proper perspective a review of published observa¬
tions in the literature was started. This is a considerable task since much of the raw
data is published in a host of publications which include symposia relevant to iono¬
spheric matters (AGARD, URSI, Satellite Beacon Meetings) without the data getting
into the periodical literature. The data base if fully examined would include observa¬
tions made along an Australian chain, thru Japan and Korea. It would include the
chain of stations along the 70 degree West meridian. Observations which should be
studied include scintillation, ground and satellite ionosonde observations as well as
in situ measurements (OGO 6, DE-2 etc.). At the present we are concentrating on the
reduction of a set of data in our hands.
The interest in middle latitude irregularities includes such diverse users as Low
Orbiting Satellites (to be instrumented at 136-150 MHz), called Little LEOs, OTH
radars and their clutter problems, and heating experiments at Arecibo Puerto Rico
and in Alaska. From the point of view of trying to understand the physical mecha¬
nisms involved little has been studied. Even the morphology and the necessary con¬
ditions for the generation of middle latitude irregularities has only been the subject
of a few research studies. There has been little done u '.derstanding the coupling of E
and F layer irregularities. We are proposing that the continuation of our work on ir¬
regularities from equatorial to high latitudes concentrate a major portion of its study
on middle latitude irregularities.
During the month of December we prepared a paper for the January meeting
of URSI. This paper originally was concerned with irregularities along a longitudi¬
nal chain in the Pacific from latitudes close to the magnetic equator to the equatorial
anomaly. The abstract was given in our last quarterly report. The data turned out to
be puzzling but consistent for the most part with the concept that the high altitude
equator plumes map along the lines of force of the earth’s field and generate irregular¬
ities at latitudes up to and including the anomaly region. However the study raised
more questions than it answered.
For latitudes somewhat higher that the anomaly region, the problem arises of
separating polewards effects of the equatorial plumes ana the equatorwards motion
of irregularity development originating in the auroral region during severe magnetic
storms. In addition to the equatorwara development of high latitude storms ana pole-
wards development of the high altitude plume irregularities, a possibility exists for
the generation of another class of F-Iayer irregularities at mid-latitudes. There exists
a body of data from Japan, Port Moresby, Osan, and Palehua, Hawaii in the Pacific
region as well as data along the 60-75 degrees West meridian.
As we stated in our last quarterly report recent OTH observations made both in
the U.S. and in Australia found that F-layer ionospheric irregularities in the south¬
ern equatorial anomaly latitudes and probably beyond that were producing clutter
on OTH units located in Northern states in the U.S. In the recent URSI Meeting in
January 1994, Dr. Gary Sales of the University of Massachusetts at Lowell indicated
that the F layer irregularities observed by the OTH radar in New England came most
probably from latitudes south of the southern equatorial anomaly. Irregularities even
at mid-latitudes can be an important part of the clutter which serious degrades OTH
In the last quarter, both Dr. Mendillo and Dr. Aarons worked up data from the
Brazilian optica! observations reported in earlier reports. The studies on magneti¬
cally quiet periods in the paper (accepted by the Journal of Atmospheric and Terres¬
trial Physics) were expanded during tnis quarter to include a study of magnetic storm
periods. The abstract for the paper on storm time irregularities is given below; it is
expected that it will be included in a COSPAR volume.
STUDIES OF STORM-TIME EQUATORIAL F-REGION IRREGULARITIES
Y. Sahai, J. Aarons, M. Mendillo, H. Takahashi, M. A. Abdu and da Paula
Observations of the F-region nightglow emissions from recombination processes
can be used to remotely observe the dynamics of the plume type of equatorial iono¬
spheric irregularities. Using a large data-base (1987-1991), the OI 630 nm emission
wide-angle imaging observations taken in the equatorial anomaly region of the Brazil¬
ian sector at times yielded effects of equatorial plumes at altitudes equal to and greater
than 2500 km. The occurrence of these high altitude equatorial ionospheric irregulari¬
ties was noted during years of high and low solar flux; the results have been presented
by Sahai etal. (1993).
In this study we present case studies of the generation or absence of depletion
regions only during the months when the occurrence of F-layer irregularities is at its
minimum (for Brazil during the months of June, July and August. We use the data
base of the OI 630 nm emission imaging and ionospheric sounding observations in
Brazil. The cases studied occurred in years of both high and low solar flux.
As expected during the months stated, depletions were not detected during the 20
nights when Kp was less than 4. In the 18 nights when Kp was 4 or greater, depletions
were generated overhead on 3 nights. Given these data the necessary conditions at
the equator for the generation of plumes have to include neutral winds, height and
electron density of the F2 layer before the onset of the storm. In addition the dynamics
of the individual storms have to be viewed (i.e. the time of maximum ring current flux,
the form of the storm, and the intensity of the magnetic storm parameters).
AASERT PROGRAM IN UPPER ATMOSPHERE AND IONOSPHERIC PHYSICS
Ms. Colerico has been working with current data analysis tools as well as writing
new utilities to facilitate in the study of equatorial plasma depletions. She has been
involved with the study of observations maae at Wake Island in August 1990, mapping
6300 A airglow data to the corresponding ALTAIR radar data. Ms. Colerico is also
involved with the fabrication of an all-sky imager which will be installed at Millstone
Hill. The imager is currently being assembled with testing to follow shortly afterward.
THE ONR SPONSORED ALL-SKY IMAGER
The fabrication of an all-sky imager for installation at Goose Bay is complete.
Several months of testing at a field site nave shown that the instrument is functioning
as designed. It is now ready for installation at Goose Bay. When weather permits, the
equipment will be installed by Boston University personnel and tested at Goose Bay.